1. Field of the Invention
The present invention relates to a fuel injection system for an internal-combustion engine and a method of controlling a fuel injection system for an internal-combustion engine.
2. Description of the Related Art
In a conventional fuel injection system for an internal-combustion engine, a fuel injector having an electromagnetically-driven fuel injection valve injects fuel a multiple number of times in each operation cycle of a cylinder (provides multiple injection) for the purpose of supplying the fuel to a combustion chamber.
A multiple injection control technology disclosed, for instance, in JP-A No. 201900/2003 provides main injection for main torque generation, pre-injection for torque reinforcement, and post-injection for gas treatment. This technology also checks whether at least one predefined condition is met. If no such condition is met, this technology decreases the number of multiple injections in accordance with priority given to multiple injection and adjusts fuel injection conditions to achieve highly reliable multiple injection.
However, while the demand for multiple injection is increasing year by year, the reinforcement of a control circuit used in a fuel injection system is limited by cost considerations. It is therefore necessary to avoid an increase in the cost of circuit configuration and provide the required number of multiple injections without sacrificing present injection characteristics.
The present invention has been made in view of the above circumstances, and provides a fuel injection system that has a simple configuration and is capable of basically providing the required number of multiple injections or gradually decreasing the number of multiple injections even when the levels of setup conditions and parameters required for fuel injection are lowered. The present invention also provides a method of controlling such a fuel injection system.